Field of the Invention
The present invention relates to a foldable display device, and more particularly, to a foldable display device capable of preventing distortion of a folding part of a display screen due to deformation of the folding part.
Discussion of the Related Art
An image display device, which realizes various pieces of information on a screen, is a core technology of the information and communication age, and is being developed in the direction of becoming thinner, lighter, more portable, and having higher performance. In response, a flat panel display device, which is thinner and lighter than a cathode ray tube (CRT), for example, an organic light-emitting display device, which controls the amount of light emitted from an organic light-emitting layer to display an image, is in the spotlight.
In an organic light-emitting display device, a plurality of pixels is arranged in a matrix form to display an image. Here, each pixel includes a light-emitting element, and a pixel drive circuit including, for example, a plurality of transistors to independently drive the light-emitting element.
Since such an organic light-emitting display device employs a self-luminous organic light-emitting element, the need for an additional light source is eliminated. In addition, since the organic light-emitting display device can be embodied as an ultrathin display device, research into an in-cell touch-type foldable display device, which employs organic light-emitting elements and includes a touch electrode array in a light-emitting cell, has been actively conducted in recent years.
The foldable display device is designed to be folded in conjunction with a display panel contained therein. In order to protect the display panel having the flexible property, the foldable display device is provided with a back cover. Accordingly, the back cover, which is disposed on the rear surface of the display panel to protect the display panel, should also be designed to be foldable.
A back cover of a related-art foldable display device includes a region corresponding to a folding part, which is made of silicon resin or the like to have a flexible structure, and a region corresponding to a non-folding part, which is made of metal, rigid plastic or the like to protect the display panel.
In the related-art foldable display device adopting the back cover, the folding part and the non-folding part are usually made of different materials. Here, because the two materials have different physical properties, such as rigidity, elasticity, flexibility and the like, and are compressed to different extents while passing through processes, there is a high possibility that unevenness is generated at the boundary surface between the two different materials. The unevenness generated between the folding part and the non-folding part causes a phenomenon whereby a display screen is transferred or distorted. Furthermore, the related-art foldable display device adopting a back cover has other problems in that the flexible folding part is curled upward or droops due to concentration of stress after being folded a number of times, and is deformed in its appearance or cured under the condition of high temperature and humidity.